This invention relates to a moving mechanism suitably usable in a high precision process such as a semiconductor lithographic process, for example, and a stage system having such a mechanism or an exposure apparatus having such a stage system.
The manufacture of semiconductor devices or the like uses an exposure apparatus of a step-and-repeat type (called a stepper) in which a pattern of an original (reticle or mask) is sequentially printed on different exposure regions on a substrate (wafer or glass plate) through a projection optical system while moving the substrate stepwise. An alternative is a step-and-scan type exposure apparatus (called a scanner) in which stepwise motion and scanning exposure are repeated so that the printing exposure is repeated to plural regions on a substrate. Particularly, the step-and-scan type uses a portion of the projection optical system which is relatively close to its optical axis and, therefore, it enables high precision and wide view angle exposure of a fine pattern.
These exposure apparatus have a stage unit (wafer stage or reticle stage) for moving a wafer or a reticle at a high speed. Here, moving the stage causes a reaction force of an inertia in response to acceleration or deceleration. If this is transmitted to a base table, it produces swinging motion or vibration of the base table. In response, the natural vibration of the mechanical system of the exposure apparatus is excited, to cause high frequency vibration, which adversely affects the high speed and high precision positioning of the stage.
Many proposals have been made to solve such a problem. Examples are U.S. Pat. Nos. 5,260,580, 5,684,856 and 6,072,183, showing systems in which a stator of a linear motor for moving a stage is supported by a floor, independently of a stage base table, thereby to prevent swinging motion of the stage base table due to a reaction force. U.S. Pat. No. 5,172,160 shows a system in which, to a machine frame for supporting a wafer stage and a projection lens, a force actuator for producing a force in a horizontal direction is used to apply a compensating force equivalent to a reaction force caused in response to the stage motion, thereby to reduce the swinging motion of the system by the reaction force.
In these examples, however, although the swinging motion itself of the stage system can be reduced, the reaction force responsive to the stage motion is transmitted directly to the floor or to the floor via a member which can be regarded as being substantially the floor. As a result, the floor is vibrated, which then causes vibration of a peripheral apparatus adjacent to the exposure apparatus. Generally, the floor on which an exposure apparatus is disposed has a natural vibration frequency of about 20-40 Hz. If the natural frequency of the floor is excited in response to the operation of the exposure apparatus, it causes large adverse influences to peripheral equipment.
The stage acceleration is becoming larger and larger due to increases of the processing speed (throughput). For a step-and-scan type exposure apparatus, for example, the largest acceleration of a stage reaches 4G (for a reticle stage) or 1G (for a wafer stage). Further, the mass of the stage is becoming bulky, due to increases in size of a reticle or a substrate. For these reasons, a driving force that can be defined by xe2x80x9cthe mass of a moving elementxe2x80x9d as multiplied by xe2x80x9cthe accelerationxe2x80x9d becomes very large and, therefore, the reaction force thereof is enormous. Thus, the reaction force becomes large with the increase of acceleration and weight, and vibration of the floor due to the reaction force cannot be disregarded.
Further, the size of the apparatus becomes large. In a manufacturing factory in which many production machines should be disposed, the area to be occupied by these machines is a problem to be considered.
On the other hand, the procedure for manufacturing semiconductor devices, constituted by a very fine pattern such as LSI or VLSI, uses a reduction projection exposure apparatus for projecting and printing a circuit pattern formed on a mask onto a substrate in a reduced scale. Increases in the density of a semiconductor device have required further miniaturization of the pattern, and many attempts have been made in exposure apparatuses in this respect.
The resolving power of an exposure apparatus can be improved by making the exposure wavelength shorter or by enlarging the numerical aperture (NA) of a projection optical system.
As regards the exposure wavelength, in place of i-line (365 nm), KrF excimer lasers having an emission wavelength near 248 nm and ArF excimer lasers having an emission wavelength near 193 nm, have been developed. Further, fluorine (F2) excimer lasers having an emission wavelength near 157 nm are being developed.
In relation to deep ultraviolet light, more particularly, ArF excimer lasers having a wavelength near 193 nm or F2 excimer lasers having a wavelength near 157 nm, it is known that there are plural oxygen (O2) absorption bands in zones close to these wavelengths. As regards fluorine excimer lasers, for example, because of the short wavelength of 157 nm, the application of it to an exposure apparatus has been attempted. However, the wavelength of 157 nm is in the wavelength region generally called vacuum ultraviolet. In this wavelength region, the absorption of light by oxygen molecules is large and, therefore, the atmosphere does not transmit most of the light. For this reason, it can be applied only in an environment in which the pressure is reduced close to vacuum and the oxygen density is made sufficiently low.
Further, the absorption of light by oxygen results in production of ozone (O3) which in turn functions to strengthen the absorption of light. Therefore, the transmission factor becomes very low. Additionally, various products attributable to the ozone are deposited on the surfaces of optical elements, causing a decrease of the efficiency of the optical system.
In consideration of this, along an optical path of an exposure optical system in a projection exposure apparatus having a light source of deep ultraviolet rays such as an ArF excimer laser or a fluorine excimer laser, purge means based on an inactive purge gas such as nitrogen, for example, is disposed to maintain a low oxygen concentration along the optical path, of an order of a few ppm or smaller.
As described, in an exposure apparatus using deep ultraviolet light, more particularly, an ArF excimer laser having a wavelength near 193 nm or a fluorine (F2) excimer laser having a wavelength near 157 nm, since the ArF excimer laser light or F2 excimer laser light can be very easily absorbed by a substance, the optical path must be purged to a few ppm order level or lower. This is also the case with water or moisture. Similarly, it must be removed to a ppm order or lower.
Thus, in order to assure a good transmission factor to ultraviolet light or a good stability of it, the path of ultraviolet light such as a reticle stage, for example, of exposure apparatuses is purged by use of an inactive gas. For example, U.S. Pat. No. 5,559,584 shows a structure in which an inactive gas is blown against a photosensitive substrate. However, in this example, purging the oxygen and water content is insufficient. Japanese Laid-Open Patent Application, Laid-Open No. 279458/1996 shows use of a closing member for covering the whole space from the bottom end of a projection optical system to a photosensitive substrate. With this structure, the motion of the stage is not easy, and it is not practicable.
It is an object of the present invention to provide an exposure apparatus by which the influence of vibration or swinging motion resulting from the motion of a stage can be reduced, and by which a high precision can be accomplished.
It is another object of the present invention to provide an exposure apparatus by which, through reduction of the influence, to the floor, of a reaction force caused in response to acceleration or deceleration of the stage, the influence which otherwise is applied to another machine or machines, disposed on the same floor, can be reduced and, also, by which the area to be occupied by the machine can be made smaller.
It is a further object of the present invention to provide an exposure apparatus which uses ultraviolet light, more particularly, ArF excimer laser light or F2 excimer laser light, wherein, because the absorption of the ArF excimer laser light or F2 excimer laser light by oxygen or water content is very large, the oxygen concentration or water concentration must be lowered to attain a sufficient transmission factor and a good stability of ultraviolet light. The present invention concerns development of effective purge means in relation to a wafer and/or a reticle, which moves along the path of ultraviolet light inside the exposure apparatus.
On the basis of these features, the present invention can provide a device manufacturing method of a good productivity, using an exposure apparatus such as described above.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.